Many conventional internal combustion engines have been configured to provide lubricating oil that sprays the cylinder walls or piston liners over which the piston rings travel during the cycle of the engine.
In some 2-cycle engines, such as the ‘Internal combustion engine with a single crankshaft and having opposed cylinders and opposed pistons’ (‘OPOC engine’) described in U.S. Pat. No. 6,170,443 and incorporated herein by reference, lubricating crankcase oil is splashed or sprayed into the cylinder area below the piston rings to effect wetting of the cylinder liner surfaces. In such lubrication systems, piston rings pick up the lubricating oil as they pass over the wetted liner surfaces and carry it forward as the piston travels from bottom dead center (‘BDC’) towards top dead center (‘TDC’). With each stroke, a small amount of oil is carried past the exhaust and inlet ports of the cylinder. By using a plurality of rings, acceptable gas sealing is accomplished to prevent high compression exhaust gases from migrating along the gap between the piston and the cylinder.
There is a need to improve the lubrication system as it applies to 2-cycle engines, since if the liner is too wet, the piston rings carry too much oil forward into the scavenging ports and into the combustion chamber. This results in loss of oil through the exhaust ports that can result in HC emissions. Also, the moving of oil past the intake ports causes some oil to be carried into the combustion chamber, which may alter the combustion process. Conversely, if not enough oil is transported to the piston rings, then excessive wear may result.
Also, it is desirable to reduce the number of upper rings within an engine and still allow efficient oil lubrication near the upper end of the piston throughout its travel, while preventing oil from migrating into the combustion chamber itself. It is further desirable to reduce the number of upper rings within an engine while preventing gas from leaking from the combustion chamber and into the oil sump. One such improvement is shown and described in U.S. Pat. No. 7,735,834, which is incorporated herein by reference. There, a non-moving oil/gas seal assembly is mounted in the cylinder wall immediately below the exhaust/intake port to ensure both gas and oil tightness. The seal assembly is in constant contact with the piston side wall throughout the piston's travel within the cylinder and utilizes a compression spring to maintain the sealing pressure of the ring against the piston side wall.
Another prior art stationary ring seal is shown in FIG. 1, wherein a one piece ring 120 is shown mounted within a ring containment groove 102 in a cylinder liner wall 101. A reciprocating piston 110 is shown having a side wall surface 111 that is mounted for reciprocating movement along an axis that is horizontal in the drawing.
For reference purposes in FIG. 1 (as well as all of the figures), the portion to the left of the oil scraper ring 120 is the ‘lower’ portion and the portion to the right of the oil scraper ring 120 is the ‘upper’ portion. These terms correspond to references made with respect to internal combustion engines where portions in the cylinder towards the combustion chamber are considered to be upper portions and those portions with reference to the combustion chamber and towards the oil sump are lower portions. Accordingly, when reference is made to locations that are ‘above’ or ‘below’ they are understood to be relative positional terms within the same directional concept.
An oil lubrication drain passage 108 is provided in the cylinder 101 to allow lubricating oil to drain from the lower portion of the cylinder side wall 106 below the seal assembly. Since a small gap exists between the side wall surface 111 of piston 110 and the side wall surface 106 of cylinder liner 101, scraper ring 120 has inwardly extending scraper blade surfaces 122 and 124 that are in contact with the piston side wall 111. The scraper blade surfaces 122 and 124 are formed in parallel rings of equal diameter. The blade surface 122 is the ‘upper’ blade because it is nearest the combustion chamber part of the cylinder from which gases G (see arrow) from the combustion chamber are present in the gap under pressure immediately after combustion. The circular upper blade surface 122 is continuous, except for the ring gap (not shown), to prevent gases G from migrating through the gap and into the lower part of the cylinder. The circular lower blade surface 124 is arcuate and discontinuous due to open gaps 125 that allow oil accumulated through the scraping process to be released below the seal. The scraper ring 120 has a single groove 126 formed on its outer circumference and a tension spring 130 is located within groove 126 to provide continuing pressure to scraper ring 120 and keep the scraper blade surfaces 122 and 124 in contact with piston side wall 111.